A known high volume liquid pump includes a casing having an inlet and an outlet and a plurality of radially spaced diffuser vanes arranged about a central vertically orientated axis within the casing and spaced from the axis. In a typical embodiment of such a pump, the inlet is defined in a bottom wall of the casing and the outlet in a side of the casing. The diffuser vanes are positioned in a region of the pump casing below a top of the casing. An impeller is mounted inward of the vanes, to rotate about the central vertical axis of the casing. A cylindrical guide sleeve, known as a casing adaptor or water guide, is mounted between the inlet and the diffuser vanes, coaxial with the central axis, to provide a conduit between the inlet and the impeller.
Pumps of the type described are used in the coolant systems of pressurised water reactors in nuclear power stations. It will be appreciated that such pumps require regular inspection of the internal surface of the casing and of the surfaces of the diffuser vanes. Further, such pumps may be radioactively contaminated.
It is known to inspect the internal surface of the casing and the diffuser vanes of a pump of the type described, by means of a remotely operated and manoeuvrable inspection device having a video camera mounted thereon, the device being mounted within the casing above the inlet. In order to mount the known device in position, a removable portion of the top of the casing is required to be removed and the impeller and the casing adaptor removed via the top of the casing.
It will be appreciated that removal of the casing adaptor is particularly difficult and time consuming and may lead to exposure to radiation. In particular, casing adaptor locking cups must be removed, followed by casing adaptor bolts. Where the casing adaptor bolts have seized, such bolts must be machined out, using a specialized device. The radioactive casing adaptor must be extracted and stored. In practice, damage to various components, such as a split ring, may occur in the removal of the casing adaptor, necessitating repair to such components. After removal of the casing adaptor, as described, and visual inspection of the internal surface of the casing and diffuser vanes, the casing adaptor must be re-installed. The casing adaptor bolts must be replaced and torqued to specification, and the locking cups replaced.
By means of the present invention the internal surface of the casing and the diffuser vanes are inspected via the diffuser vanes, thereby obviating removal of the casing adaptor. By eliminating the need for removal of the casing adaptor, down time of the reactor is reduced. Also, the need to machine-out seized bolts and retrieve components such as broken locking cups which have fallen into the casing, in obviated. Further, the possibility of incorrect torquing of the bolts or replacement of the locking cups is eliminated.